Personal computers (PCs) have permeated nearly all levels of society and business, creating a need to link individual PCs into networks to more efficiently utilize and share resources. Computer networks are becoming increasingly popular in low-cost, performance-oriented computing environments.
One very popular type of network used to link PCs or workstations is called a local area network (LAN). LANs and other types of networks permit the sharing of resources such as software, printers, modems, and other peripherals among PC workstations operating as nodes on the network.
FIG. 1 illustrates a simple and conventional LAN, generally designated by the reference numeral 100. Network 100 comprises a plurality of PC workstations 112a through 112e, each connected by a communication link 113a through 113e respectively to an associated hub 114. Communication links in such networks are typically two-conductor cables, wherein a potential across the two conductors is varied in a manner representing sequential binary data. Such a link is termed a serial link.
Hubs, such as hub 114, in networks are used to connect multiple workstations for routing through a single link to a server. In FIG. 1, PC workstations 112a through 112e are all connected to server 116 through link 115. Hubs typically have a limited number of input ports, so the number of workstations that can be connected is limited as well. Typically the input ports are arranged in groups of 8, 16, 32, 64 and so forth. Further network capacity can be added by connecting multiple hubs, such as hub 118 (shown in dashed lines) to the one file server, and the additional hubs may then be connected to other multiple workstations (not shown). Other network variations include addition of multiple file servers connected in different arrangements to multiple hubs.
File server 116 in this example, and generally in the art, comprises a set of sheared high-capacity mass storage devices, such as hard disks. Such file servers are often special PCs that have higher performance capability and more and larger capacity hard disks than do individual workstations 112a through 112e. The shared disk space on such file servers typically stores software applications which spreads the cost of the hard disk over more than one user, thereby permitting more efficient use of resources.
File server 116 in this example may also contain routers (not shown) for communication and connection to different network protocols such as Ethernet.TM., Asynchronous Transfer Mode (ATM), and Fiber Distributed Data Interface (FDDI), among others. The output of file server 116 is coupled to shared peripherals such as a network modem 118, a laser printer 120, and other peripherals represented by element number 122. All workstations 112a through 112e on the network share access to the peripherals connected to server 116.
It will apparent to those with skill in the art that the example of FIG. 1 is but one of many network arrangements known in the art.
There are some limitations of a conventional LAN 100 as described above. For example, communication over link 115 is shared by all of the workstations, and if many workstations are attempting to communicate at once, bandwidth may be a problem, slowing communication. By way of example, coaxial lines used in many networks have a maximum data transfer rate of 10 megabytes per second (Mb/s). The maximum data transfer rate, which is related to bandwidth, ultimately determines the maximum number of workstations that can be adequately handled by the network. Overloading a network can result in lost connections, communication delays, slow system response, timeouts, and slow file transfer times. All of these situations decreases the efficiency of the network, and become very annoying to network users.
Another limitation of conventional LANs such as LAN 100, is that communication collisions may occur between multiple workstations requesting access to the network. In commonly used network protocols such as Ethernet.TM., one way that collisions are handled is by processing one request at-a-time while buffering other requests in a first-in-first-out (FIFO) buffer. Since access is granted one-workstation-at-a time, other stations are required to wait, thereby decreasing efficiency. Networks with heavy traffic tend to have many collisions which may drop efficiency to unacceptable levels.
The problems of inefficient communication are exacerbated by addition of more workstations to the network and increased use of bandwidth-hungry applications such as color publishing and document imaging. So networks that had adequate bandwidth when installed may be outdated simply by software development.
Another way to add bandwidth is by increasing the number of switching hubs. This solution often results in segmenting a single large network into multiple smaller networks, which decreases the amount of traffic that travels over any given communication link and thereby increases the bandwidth available to each individual user. Statistics and traffic patterns can be further analyzed for adjustments for optimal network performance.
Another disadvantage of conventional networks is the relatively high cost of multi-port hubs. By way of example, a 32 or even 16 port hub for some networks can cost in the range of about 32K to 100K dollars, a substantial investment for any user. Also conventional hubs are typically separate units in an enclosure with a dedicated power supply and controlling electronics, adding to clutter and adding to cost.
What is needed is a switchable hub that is relatively low cost, compact, and increases network performance by increasing bandwidth and reducing collisions. As will be described hereinafter, the present invention provides a method and apparatus to meet these objectives.